The concept of the airway as a distinct biological compartment with cytokine levels differing from those in the systemic circulation is supported by other studies: Hollander et al. [28] found that the concentrations of IL-8 and of other markers of inflammation were significantly higher in BAL samples compared to serum samples in patients with bronchial asthma and COPD. Here, CXCL8 is linked to chronic obstructive pulmonary disease.